Optimizing microwave frequencies for hydrogen and electromagnetic shielding materials production through methane pyrolysis over biochar
Mengyuan Wen, Yijie Liu, Jurong Ren, Jia Wang, Jianchun Jiang
Abstract
Clean hydrogen production through methane pyrolysis over renewable biochar offers a promising avenue for sustainable energy generation. Herein, an innovative approach that utilizes variable microwave frequencies to facilitate methane pyrolysis is introduced. The frequency optimization study reveals that a frequency of 4225 MHz maximizes methane conversion, yielding an impressive rate of 90.7 % at 100 W microwave power. However, prolonged pyrolysis under the same frequency for 60 min leads to a diminished conversion, resulting in a reduced efficiency of 43.9 %. Notably, by alternating microwave frequencies to 4400, 5150, 4600, and 4620 MHz, the reactivation of deactivated biochar is achieved, consistently restoring efficiency to over 97 % for five consecutive cycles. The transition from polarization-driven loss to conduction-induced loss is identified as the key mechanism responsible for the in-situ reactivation of spent biochar, which is controlled by varying microwave frequencies. Moreover, the spent biochar exhibits a heightened microwave-absorbing capacity, characterized by an exceptionally low reflection loss of −73.1 dB at a thickness of 2.1 mm. Hence, adjusting microwave frequencies to enhance methane pyrolysis not only promotes clean hydrogen production but also yields high-performance electromagnetic shielding materials. This dual outcome optimizes sustainable methane pyrolysis for efficient hydrogen production.